King crabs' diets vary with their age and the depth at which they live in the ocean. Larval crabs float around and eat plankton, juvenile crabs fall to the ocean floor and eat other organisms that live there, and adults eat worms, bivalves, echinoderms and algae.
King crabs eat a wide assortment of marine life. Worms, clams, mussels, snails, brittle stars, sea stars, sea urchins and sand dollars are consumed by king crabs as well as barnacles, crabs, other crustaceans, fish parts, sponges and algae, according to Bahr's Landing. In the Barents Sea, the king crab is an invasive specie that eats almost everything it encounters.